Possibly because the arrogant and obnoxious have no problem doing what most people would not allow themselves to do.
Most Urapmin spend their lives trying to find balance between wilfulness and lawfulness. Moving back and forth between their two values, most people never realise either one completely, but at the same time, they never fail to fulfil each of them in partial ways. I think Kinimnok captivated other Urapmin because he showed them what wilfulness in its fullest form looks like. Most of them would never follow him in realising wilfulness so absolutely, but in Kinimnok they saw what wilfulness looked like when it was given free expression.
Meanwhile, in other political matters